The objective of this proposal is to develop non-invasive diagnostic methods for 1. the assessment of pulmonary hypertension, 2. the detection and assessment of early degeneration of porcine xenograft aortic prosthetic valves, and 3. the detection and assessment of early stages of aortic valvular degeneration. Each of these non-invasive diagnostic methods will be based upon measurements of the amplitude and/or frequency of the second heart sound. Recent studies in our laboratory have clearly shown that the second heart sound results from diastolic vibration of the closed semilunar valves. Mathematical modeling of vibration of a simplified model of the semilunar valve has identified the various factors which affect the amplitude and frequency of the acoustical signal. These pathophysiological and hemodynamic factors were evaluated in circulatory models of the cardiovascular system, in dogs, and in patients. Thus, through a mechanistic approach we have identified factors that affect the second heart sound. These investigations indicated that the amplitude of the pulmonary component of the second sound would be affected by hemodynamic factors which in turn are affected by pulmonary arterial pressure. Both the amplitude and frequency of the aortic component of the second sound (or aortic xenograft component of the second sound) would be affected by valve stiffness. Therefore, there is clear justification to expect that measurement of the amplitude and/or frequency of the second sound would permit an assessment of pulmonary hypertension and of early degeneration of aortic or xenograft valves. Measurements of the amplitude and frequency of sound at the chest wall will be accomplished with calibrated sound transducers and a real time spectral analyzer. Assessments of sound amplitude and frequency will be evaluated on the basis of pulmonary pressures and left ventricular hemodynamics and aortograms obtained during cardiac catheterization. The amplitude and frequency of intracardiac sound will also be measured to determine the extent to which sound transmission affects the predicted observations.